It is frequently necessary to sample or remove a sample from a suspect tissue for testing. In humans, such a sample removal is particularly useful in diagnosis and treatment of cancerous or pre-cancerous conditions. In the case of suspected cancer, particularly cancer of the breast, early detection and diagnosis is critical to the success of the patient's treatment and recovery.
Various techniques are available to aid in detection and diagnosis, including physical examination and imaging, such as mammography, x-ray, ultrasound, magnetic resonance imaging (MRI), and the like. When a condition is detected that suggests the possibility of cancer, a biopsy can be performed to obtain tissue samples for a complete diagnosis.
One biopsy technique frequently performed is a core biopsy, which uses a core biopsy device in which a cannula is inserted into the tissue of interest, thereby coring a biopsy sample from the tissue having a cross section similar to that of the cannula, and which is retained within the cannula. The cannula, with the biopsy sample, is then removed from the tissue, followed by cytological and/or histological analysis of the sample.
One group of core biopsy devices is based on the combination of a notched inner stylet and an outer severing cannula. The stylet is retained within the lumen of the outer cannula such that the pointed end of the stylet closes off the open end of the cannula. The stylet and cannula are advanced into the tissue mass until they are near the desired biopsy site. The stylet is then advanced relative to the outer cannula to expose the notch to the biopsy site where the tissue prolapses into the notch. The outer cannula is then advanced to sever the tissue in the notch. The disadvantage of this method is that it produces a small core biopsy relative to the outer cannula size since the cross section of the sample is substantially smaller than the cross section of the outer cannula. The advantage of this method is that the sample is completely severed from the tissue mass and securely retained within the notch.
Another group of core biopsy devices is based on a coring cannula in combination with a non-notched stylet. The stylet is used to plug the end of the coring cannula during the insertion of the coring cannula into the tissue adjacent the biopsy site. The coring cannula is then advanced relative to the stylet into the biopsy site to retain a sample within the coring cannula. The advantage of this device is that a full core biopsy sample is obtained. That is, the cross section of the sample is substantially equal to the cross section of the coring cannula. The full core sample provides a much larger sample which is highly advantageous.
The disadvantage of this full core biopsy device is that the end of the sample is not positively severed from the tissue mass, creating the possibility that the biopsy sample will be pulled out of the coring cannula upon the withdrawal of the coring cannula. This can happen if the forces holding the sample in the coring cannula are not sufficient to tear the end of the sample from the tissue mass. Since the sample normally comprises wetted tissue that completely fills the coring cannula, the suction force and/or the frictional force between the tissue sample and the inner wall of the coring cannula are the dominate forces for retaining the sample in the cannula. However, if these forces are not sufficient to tear the end of the sample from the tissue mass, the sample will be pulled out of the coring cannula upon the removal of the coring cannula. Some practitioners pivot the biopsy device in hopes that the end of the cannula will at least partially sever the attached portion of the sample. However, this is not preferred as it increases the damage to the remaining tissue.
Another disadvantage of all of the full core devices is that they rely on the relative movement between the coring cannula and the stylet to expel the sample from the interior of the coring cannula. The use of the stylet to force out the sample can damage the sample. The damage can be great enough to render the sample unsuitable for testing. This can be very detrimental since some lesions being sampled are small enough that the entire lesion is contained within the sample. For larger lesions, some practitioners will take multiple samples to allow for potential damage of one of the samples. This practice increases the invasiveness of the procedure and the pain to the patient.
While there have been many attempts in the art to produce a workable core biopsy device, there is still a strong need for a core biopsy device that minimizes patient discomfort, insures a complete excision of the biopsy sample from the surrounding tissue, enables the biopsy sample to be removed from the device without disturbance of the sample, and is simple and cost effective to manufacture.